Determination of the effective lens position of an intraocular lens using aphakic refractive power

ABSTRACT

An ophthalmic method for determining a relationship between aphakic ocular power and estimated effective lens position (ELP) of an intraocular lens (IOL) to be implanted in a patient&#39;s eye. The method can be used to determine an estimate of the ELP of an IOL given the aphakic ocular power of the patient&#39;s eye, for example, without measurement of the corneal curvature or axial length of the patient&#39;s eye. The estimate of ELP can then be used to determine a suitable value of optical power for the IOL to be implanted in the patient&#39;s eye.

This application claims priority to U.S. Provisional Patent Application61/225,532, filed Jul. 14, 2009, and entitled “DETERMINATION OF THEEFFECTIVE LENS POSITION OF AN INTRAOCULAR LENS USING APHAKIC REFRACTIVEPOWER,” which is hereby incorporated by reference herein in itsentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The field of the invention relates to ophthalmic systems and procedures.In particular, the field of the invention relates to the determinationof the post-surgical effective lens position (ELP) of an intraocularlens (IOL) and IOL power.

2. Description of the Related Art

Cataracts are clouded regions that can develop in the naturalcrystalline lens of an eye. A cataract can range in degree from slightclouding to complete opacity. Typically, formation of cataracts in humaneyes is an age-related process. If left untreated, cataracts can lead toblindness. Surgeries have been developed for the treatment of cataractsby replacement of the natural crystalline lens with an artificial lens.Typically, an incision is made in the eye and the natural crystallinelens is removed. An artificial implant called an intraocular lens (IOL)is then inserted, for example, in the capsular bag of the eye in placeof the natural crystalline lens. The spherical and/or astigmatic opticalrefractive power of the IOL may be selected so as to give the eye adesired amount of post-surgical refractive power. For example, the powerof the IOL may be selected so as to place the eye in a substantiallyemmetropic state when combined with the refractive power of the corneaof the eye.

SUMMARY OF THE INVENTION

In some embodiments, a method for determining the optical power of anintraocular lens to be inserted into the eye of a patient comprises:receiving as an input an indication of the aphakic refractive power ofthe patient's eye; determining, with a processor, an estimate of thepost-surgical effective lens position (ELP) of the intraocular lens forthe patient's eye, the estimate being based on the indication of theaphakic refractive power of the patient's eye and on a relationshipbetween aphakic refractive power and post-surgical intraocular lens ELP;and determining an amount of optical power for the intraocular lens tobe inserted into the patient's eye based on the estimate of thepost-surgical ELP of the intraocular lens in the patient's eye.

In some embodiments, a computer-readable medium comprises instructionsthat, when read by a computer, cause the computer to perform a methodcomprising: receiving as an input an indication of the aphakicrefractive power of the patient's eye; determining an estimate of thepost-surgical effective lens position (ELP) of the intraocular lensbased on the indication of the aphakic refractive power of the patient'seye and on a relationship between aphakic refractive power andintraocular lens ELP; and determining an amount of optical power for theintraocular lens to be inserted into the eye of the patient based on theestimate of the post-surgical ELP of the intraocular lens.

In some embodiments, an ophthalmic method for determining a relationshipbetween post-surgical effective lens position (ELP) of an intraocularlens and aphakic ocular power comprises: obtaining a plurality ofindications of the aphakic power of a respective plurality of eyes;determining a plurality of indications of the post-surgical ELP of anintraocular lens for the respective plurality of eyes; and determining arelationship between the plurality of indications of the aphakic powerand the plurality of indications of the post-surgical ELP using aprocessor.

In some embodiments, an ophthalmic instrument comprises: a measurementdevice for measuring the aphakic power of a patient's eye; and aprocessor for performing a method comprising, receiving an indication ofthe aphakic refractive power of the patient's eye from the measurementdevice, determining an estimate of the post-surgical effective lensposition (ELP) of an intraocular lens to be inserted in the patient'seye, the estimate of the post-surgical ELP of the intraocular lens beingbased on the indication of the aphakic refractive power of the patient'seye and on a relationship between aphakic refractive power andintraocular lens ELP, and determining an appropriate amount of opticalpower for the intraocular lens to be inserted into the patient's eyebased on the estimate of the post-surgical ELP of the intraocular lens.

BRIEF DESCRIPTION OF THE DRAWINGS

For purposes of summarizing the disclosure, certain aspects, advantagesand features of the invention have been described herein. It is to beunderstood that not necessarily all such advantages may be achieved inaccordance with any particular embodiment of the invention. Thus, theinvention may be embodied or carried out in a manner that achieves oroptimizes one advantage or group of advantages as taught herein withoutnecessarily achieving other advantages as may be taught or suggestedherein. Certain embodiments are illustrated in the accompanyingdrawings, which are for illustrative purposes only.

FIG. 1 is a plot of implanted IOL power versus aphakic ocular power fora sample group of eyes that underwent cataract surgery;

FIG. 2 is a plot of estimated ELP versus aphakic ocular power for thesample group of eyes, the estimated ELP having been determined using theHolladay 1 formula;

FIG. 3 is a plot of estimated ELP versus aphakic ocular power for thesample group of eyes, the estimated ELP having been determined using theHolladay 1 formula and corrected to reduce errors attributable torelatively long axial length;

FIG. 4 is a plot of three different types of estimated ELP versusaphakic ocular power for the sample group of eyes, the three differenttypes of estimated ELP being the Holladay 1 formula, the SRK/T formula,and the Hoffer Q formula;

FIG. 5 is a plot of aphakic ocular power versus axial length;

FIG. 6 is a plot of aphakic ocular power versus corneal curvature;

FIG. 7 is a plot of three different types of estimated ELP versus axiallength, the three different types of estimated ELP being the Holladay 1formula, the SRK/T formula, and the Hoffer Q formula; and

FIG. 8 is a plot of estimated ELP versus aphakic ocular power for thesample group of eyes, the estimated ELP having been determined using theHoffer Q formula and adjusted by reducing the effect of themanufacturer's constant for the IOL on the result.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In a typical cataract surgery, a surgeon removes the natural crystallinelens from a patient's eye and an intraocular lens (IOL) is implanted inits place. By selecting an IOL having an appropriate amount of sphericaland/or cylindrical power, an eye that prior to the surgery was, forexample, myopic (near sighted), hyperopic (far sighted), and/orastigmatic can be restored to, for example, an emmetropic condition. Thedetermination of an appropriate amount of IOL optical power for a givenapplication is a significant aspect of obtaining satisfactory surgicaloutcomes for patients. Various factors can be considered whencalculating the appropriate power for the IOL, such as 1) the axiallength of the eye, for example, measured from the cornea to the retina;2) the total optical power of the cornea, including its anterior andposterior surfaces; 3) the desired postoperative optical power (e.g.,0.0 diopters (D) of defocus for an emmetropic eye); and 4) the effectivelens position (ELP) of the IOL, which can be understood, for example, asthe distance from the corneal surface to the post-operative position ofthe IOL (e.g., the distance from corneal apex to the center of the IOLin its settled position).

Preoperative biometry measurements can be used to measure the axiallength of the eye and the curvature of the anterior surface of thecornea. The axial length of the eye can be measured, for example, by anultrasound device or by Optical Coherence Tomography (OCT), while thecurvature of the anterior surface of the cornea can be measured by, forexample, a keratometer (e.g., K values measured in orthogonal meridiansthat pass through the corneal apex, or anatomical center, of the corneaand are expressed in terms of the radii of curvature or as the dioptricpower of the cornea along these orthogonal meridians) or cornealtopographer (simulated K values). The total optical power of the corneacan then be estimated from the corneal curvature K values.

The ELP of the IOL affects the total refractive power of thepost-surgical eye because of the differing amount of vergence it impartsto light in the eye depending upon its spatial position between thecornea and the retina. For example, a 20 diopter IOL that is axiallydisplaced from the predicted ELP by only 0.5 mm could result in a 1.0diopter error in postoperative refraction.

The ELP of the IOL has traditionally been difficult to determine. Theposition of the natural crystalline lens in a patient's eye can bemeasured. However, since transformation of the young crystalline lensinto a cataract occurs somewhat differently from patient to patient,measurement of the position of the crystalline lens (cataract) prior tosurgery often does not lead to an accurate determination of the ELP.Therefore, other methods for estimating ELP have been developed.

Early on, a fixed value was used for all eyes as an estimate of ELP, andthe resulting residual refractive error was treated with glasses orcontact lenses. Later, estimates of ELP were developed based on biometrydata, such as measurements of the axial length and corneal curvature ofthe patient's eye. The estimation of ELP can also be based on horizontalcorneal diameter, anterior chamber depth, lens thickness, preoperativephakic ocular refraction, and patient age. There are mathematicalformulas for estimating ELP based on these factors. Such formulasinclude, for example, the Holladay 1, SRK/T, Hoffer Q, Holladay 2, andHagis formulas. These formulas are used to calculate IOL power. However,these formulas generally only differ in the specific method used forestimating ELP. Therefore these formulas may be referred to as IOL powercalculation formulas or ELP estimation formulas.

The Holladay 1, SRK/T, and the Hoffer Q formulas are consideredsecond-generation formulas. The Holladay 2 and the Hagis formulas areconsidered third-generation formulas. An article entitled “Accuracy ofintraocular lens power prediction using the Hoffer Q, Holladay 1,Holladay 2, and SRK/T formulas,” by Narvaez, et al., appeared in theDecember 2006 issue of the Journal of Cataract & Refractive Surgery. Thearticle compared the effectiveness of these four IOL power formulas fora group of patients. The results presented below show that the threesecond-generation formulas are generally as effective as the Holladay 2,which uses more of the above-named variables.

Mean Absolute Difference, Predicted Versus Actual Axial LengthPostoperative SE Refraction (D) ± SD (mm) Eyes Holladay 1 Holladay 2Hoffer Q SRK/T <22.0  14 0.85 ± 0.58 0.90 ± 0.67 0.72 ± 0.48 0.91 ± 0.5822.0 to <24.50 236 0.57 ± 0.45 0.56 ± 0.44 0.58 ± 0.46 0.56 ± 0.45 24.5to 26.00   72 0.50 ± 0.38 0.46 ± 0.36 0.51 ± 0.36 0.49 ± 0.38 >26.00 160.78 ± 0.73 0.65 ± 0.76 0.75 ± 0.70 0.65 ± 0.83 All eyes 338 0.58 ± 0.460.56 ± 0.46 0.58 ± 0.46 0.57 ± 0.47

As the technology surrounding cataract surgeries continues to improve,increasingly, patients have expectations of being spectacle free aftercataract surgery. In order to achieve emmetropic results for patients,there is a need to improve ELP estimation.

Since the accuracy of the ELP estimation is dependent upon the accuracyof the biometry measurements which are input into the formula, thelarger the number of measurement inputs that are used in the ELPestimation formula, the greater the opportunity for measurementinaccuracies to be introduced. There is potential for mistakes to occurin each biometry measurement that is made. Thus, it would be desirableto reduce the number of measurements needed as inputs for an ELPestimation formula.

In addition, the use of keratometry measurements in ELP estimationformulas may be problematic in the case of patients who have hadprevious refractive surgery (e.g., RK, PRK, LASIK, etc.). Typically, thetotal power of the cornea is determined from keratometer readings of thefront surface of the cornea based on a valid assumption regarding therelationship between the front surface of the cornea and the backsurface of the cornea. To correct a person's ocular refractive error,various refractive surgery procedures change the shape of the frontsurface of the cornea. Thus, determining the total corneal power fromthe keratometer measurement may not be clinically valid for postrefractive surgery patients. Numerous formulas have appeared in theophthalmic literature purporting to most accurately estimate totalcorneal power based on keratometer readings for post refractivepatients. However, the accuracy of these formulas for estimating totalcorneal power is not proven. Since refractive surgeries that alter theshape of the cornea have become relatively common, this problem affectsa significant number of cataract patients. Thus, it would be beneficialto reduce or eliminate the dependence of ELP estimates on keratometricmeasurements.

Systems and methods are described herein, which, in some embodiments,eliminate the need for total corneal power and axial lengthmeasurements. Instead, total corneal power and axial length are replacedby an indication of aphakic ocular power. In some embodiments, an ELPestimation formula is provided that does not receive total corneal powerand axial length measurements as inputs but instead receives anindication of aphakic ocular power. In some embodiments, the indicationof aphakic ocular power is an intraoperative direct measurement of theaphakic ocular power of the patient's eye.

In some embodiments, the direct measurement of aphakic ocular power ismade using a wavefront aberrometer (e.g., Talbot-Moiré, Shack-Hartmann,or others), though other instruments can also be used. The wavefrontaberrometer may be mounted to, and optically aligned with, a surgicalmicroscope used by the surgeon to perform the cataract surgery. Such adevice is described in US Patent Publication 2005/024327, whichcorresponds to co-pending U.S. patent application Ser. No. 11/110,653,filed Apr. 20, 2005 and entitled “INTEGRATED SURGICAL MICROSCOPE ANDWAVEFRONT SENSOR.” One type of wavefront aberrometer that is suitablefor performing the types of intra-operative measurements describedherein is a Talbot-Moiré wavefront aberrometer such as the one describedin U.S. Pat. No. 6,736,510, issued May 18, 2004 and entitled “OPHTHALMICTALBOT-MOIRÉ WAVEFRONT SENSOR.” The foregoing references are both herebyincorporated by reference in their entirety.

Briefly, the Talbot-moiré wavefront aberrometer functions by introducinga probe laser beam into the patient's eye. The probe laser beam can bealigned to be coincident with the visual axis of the patient's eye, forexample. The probe laser beam passes through the cornea, including theanterior and posterior surfaces, and is incident upon the retina. Theprobe beam scatters from the retina, for example, in such a way as tobehave as a point source of light at the retina. The scattered probebeam light passes back through the eye, including the cornea. Theoptical wavefronts of the probe beam are altered according to therefractive properties of the eye (e.g., according to the shapes of theanterior and posterior surfaces of the cornea). The altered wavefrontcan then be analyzed to determine the optical power of the eye,including, for example, spherical power, astigmatic power, andastigmatic axis.

The aphakic ocular power of a patient's eye is dependent upon the totalcorneal power and the axial length of the patient's eye. In fact, atheoretical aphakic ocular power value can be calculated from cornealpower and axial length data. However, in some embodiments, it isadvantageous to instead measure aphakic ocular power directly and to usethis measurement to estimate the ELP of the IOL for several reasons.First, a direct measurement of aphakic ocular power is not dependentupon a formula for estimating total corneal power from the curvature ofits anterior surface. As discussed herein, the accuracy of such anestimate suffers in the case of patients who have had prior refractivesurgery. Instead, the aphakic ocular power measurement actually measuresand accounts for the optical power contribution of both the anteriorsurface and the posterior surface of the cornea even in cases where theanterior surface has been altered in a separate refractive surgery; itdoes not rely upon a modeled relationship between the respective shapesof the two corneal surfaces.

Second, since the aphakic ocular power measurement can be made throughthe pupil, for example, with respect to the visual axis of the patient'seye, rather than the optical axis, then the contribution of totalcorneal power to the aphakic ocular power measurement corresponds to theoptical power that the patient actually experiences through the eye. Incases where, for example, the pupil is not centered on the anatomicalcenter of the cornea, the corneal power measured with respect to thevisual axis of the eye can be different than the corneal power measuredwith respect to the anatomical center of the cornea, as may be done witha keratometer.

Third, the ability to replace the corneal power and axial lengthmeasurements with a single measurement of aphakic ocular power reducesthe number of measurements that need to be made to provide input datafor the estimation of ELP. This in turn reduces opportunity for error tobe introduced in the measurements. It may also reduce the amount of timefor pre-operative diagnostics.

In some embodiments, a cataract surgery is performed by removing thenatural crystalline lens from the patient's eye. In some embodiments,preoperative biometry measurements of the corneal curvature and axiallength are not required. Instead, a surgeon measures the aphakic ocularpower of the patient's eye during the surgery once the naturalcrystalline lens has been removed. As discussed herein, the aphakicocular power can be effectively substituted for measurement datarelating to the corneal power and axial length of the patient's eyesince aphakic ocular power depends upon these two characteristics of theeye.

Once the aphakic ocular power of the eye (e.g., spherical power,cylindrical power, spherical equivalent power, etc.) has been obtained,it can be used to determine an estimate of the ELP of the IOL. Theestimated ELP can then be used to determine IOL power using a refractiveIOL power formula that is a function of, for example, aphakic sphericalequivalent power (SE=sphere value+½ the cylinder value) and of the ELPestimate. The IOL power formula may also be a function of Kmeasurements, though the ultimate dependence of IOL power on Kmeasurements is reduced due to the reduced dependence of the ELPestimate on K measurements.

IOL power can be calculated, for example, according to the followingformula, where “Desired_PostRx” is the desired post-operative refractionand the “V” in each term is the vertex distance (e.g., 0 mm for“Aphakic_SE” and 13 mm for “Desired_PostRx”):

${IOLPower} = {\frac{1336}{\frac{1336}{\frac{1000}{\frac{1000}{Aphakic\_ SE} - V} + K} - {ELP}} - \frac{1336}{\frac{1336}{\frac{1000}{\frac{1000}{Desired\_ PostRx} - V} + K} - {ELP}}}$

Once the IOL power has been determined, the surgeon can select anappropriate IOL, implant it in the capsular bag, and complete thesurgery.

In some embodiments, as described herein, ELP is estimated from aphakicocular power, for example without using direct measurements of cornealpower and axial length. This can be done by receiving as an input anindication of the aphakic refractive power of the patient's eye. Theindication of aphakic refractive power of the patient's eye can be, forexample, a direct intraoperative measurement of the aphakic ocularpower. Such a measurement can be obtained using, for example, thewavefront aberrometer described herein. Then, an estimate of thepost-surgical effective lens position (ELP) of the intraocular lens forthe patient's eye can be determined using, for example, processingelectronics.

The estimate of ELP can be calculated from aphakic power based on arelationship (e.g., a mathematical function) between aphakic refractivepower and post-surgical intraocular lens ELP. For example, therelationship between aphakic refractive power and post-surgicalintraocular lens ELP may be expressed mathematically where ELP iswritten as a function of aphakic ocular power. Finally, the appropriateoptical power for the intraocular lens to be inserted into the patient'seye can be determined based on the estimate of the post-surgical ELP ofthe intraocular lens in the patient's eye. The estimated ELP and/or theIOL power can then be output to the surgeon to be used in the selectionof a suitable IOL for the patient's eye.

As just described, determining IOL power from aphakic ocular power mayinvolve estimating ELP based on aphakic ocular power and, in someembodiments, not based on measurements of corneal curvature and axiallength. In some embodiments, determining a relationship between ELP andaphakic ocular power can be accomplished by obtaining indications of theaphakic power of a plurality of eyes. For example, the plurality of eyescan be a statistically significant sample size of eyes upon whichcataract surgeries have been performed. In some embodiments, theindications of aphakic refractive power for the plurality of eyes aredirect intraoperative measurements of the aphakic ocular power of theeyes. In some embodiments, the indications of aphakic ocular power forthe plurality of eyes are calculated values of theoretical aphakicocular power determined from corneal power and axial length data.

Next, indications of the post-surgical ELP of an intraocular lens in theplurality of eyes can be determined. This can be done, for example, bymeasuring post-surgical ELP of the IOL in the sample group of eyes usingultrasound or optical coherence tomography. Alternatively, oradditionally, the indications of post-surgical ELP can be ELP estimatescalculated using ELP estimation formulas, such as those described herein(e.g., the Holladay 1, Holladay 2, Hoffer Q, or SRK/T formulas).Finally, a processor can be used to correlate the indications of theaphakic ocular power of the eyes with the respective indications of thepost-surgical ELP. The processor can also be used to determine amathematical function that adequately describes the relationship betweenaphakic ocular values and the ELP values. The mathematical relationshipcan relate, for example, ELP as a function of aphakic ocular power. Thisfunction can then be used to determine an estimate of the ELP of an IOLfor a patient's eye that is outside of the sample set.

These and other methods are illustrated with respect to FIGS. 1-8, whichwill now be described in detail. Unless otherwise noted, the datadescribed herein and with respect to FIGS. 1-8 is based on a particularIOL intended to be inserted in the capsular bag of an eye. However, thesystems and methods described herein are applicable to any type of IOL.In addition, the systems and methods described herein are applicable toIOLs intended to be inserted at other locations in the eye (e.g., theanterior chamber or the sulcus).

FIG. 1 is a plot 100 of implanted IOL power versus aphakic ocular powerfor a sample group of eyes that underwent cataract surgery. Theimplanted IOL power values are plotted on the axes as a function ofaphakic ocular power, and are indicated on the plot 100 as triangles.While in some embodiments the measure of aphakic ocular power is thespherical equivalent power of the aphakic eye, in other embodiments themeasure of aphakic ocular power can be the spherical power, thecylindrical power, or some other combination of the two (other thanspherical equivalent power).

In this case (and in FIGS. 2-6 and 8), the aphakic ocular power valuesare theoretical aphakic spherical equivalent values calculated fromcorneal power and axial length data for each of the eyes. However,actual direct aphakic ocular power measurements obtainedintraoperatively for each of the eyes could have been used instead.

In this particular sample set of eyes, the aphakic ocular power valuesrange from approximately 2.5 diopters to approximately 17 diopters. Eachof the plotted aphakic ocular power values corresponds to one of 105eyes that made up the sample set. Each aphakic ocular power value (shownas the amount of power needed to correct the aphakic eye) is plottedversus the implanted IOL power that was selected in the cataract surgeryfor the corresponding eye. The aphakic ocular power data and theimplanted IOL power data were analyzed with regression techniques todetermine a fitted line 110. The fitted line 110 shows the empiricalrelationship between the aphakic ocular power data and the implanted IOLpower data. Thus, the equation of the line 110 can be used to determinethe power of an IOL to be inserted into an eye having a specifiedaphakic ocular power, or vice versa. The line 110 is of the form y=ax+b,where a and b are constants. In the equation, y corresponds to theimplanted IOL power and it is written as a function of x, whichcorresponds to the aphakic ocular power. For the particular IOL type,measurement units, and sample set of eyes that were used, the equationof the fitted line was found to be y=1.3119x+3.3871, though theconstants a and b will vary depending, for example, on these factors.

As indicated on the plot 100, there is a relatively good correlationbetween the aphakic ocular power and the implanted IOL power(R²=0.9422), thus indicating that aphakic ocular power is a relativelygood explanatory variable for implanted IOL power. However, FIG. 1 alsoshows a dotted box 120 around the fitted line 110. The dotted box 120shows the range of implanted IOL power values that are within ±0.5diopters of the value predicted by the equation for the fitted line 110.As illustrated, a relatively large percentage of the implanted IOL powervalues lies outside of this ±0.5 diopter range, meaning that if theimplanted IOL power value had actually been selected based on theillustrated mathematical relationship (i.e., the fitted line 110), thesurgery would have resulted in a possible residual refractive error ofgreater than 0.5 diopters.

The error between the IOL power values predicted based upon aphakicocular power (i.e., the line 110) and those IOL power values that wereactually used (i.e., the plotted triangles) is attributable, at least inpart, to the fact that the illustrated relationship does not account forthe ELP of the IOLs. As discussed herein, the ELP of the IOL has aclinically significant effect on the refractive power of thepseudophakic eye after the IOL has been inserted. Therefore, in someembodiments, it would be desirable to determine a relationship betweenaphakic ocular power and ELP. In some embodiments, such a relationshipcould be used to improve the accuracy of IOL power values calculatedbased on aphakic ocular power values, as indicated in FIG. 1.

FIG. 2 is a plot 200 of estimated ELP versus aphakic ocular power forthe sample group of eyes, the estimated ELP having been determined usingthe Holladay 1 formula. The estimated ELP values are plotted on the axesas a function of aphakic ocular power. These values are indicated asdiamonds on the plot 200. In some embodiments, the aphakic ocular powervalues are the spherical equivalent optical power of the aphakic eyes.In other embodiments, the aphakic ocular power values can be thespherical aphakic optical power, the cylindrical aphakic optical power,or some other combination of the two.

The aphakic ocular power values can be actual directly-measured aphakicocular power values obtained from the eyes intraoperatively. In suchcases, it is advantageous for the aphakic ocular power values of thesample eyes to span the meaningful range of aphakic ocular power valuesin the population in a statistically-meaningful way.

Alternatively, as was the case here, theoretical aphakic ocular powervalues calculated from corneal power and axial length data for the eyesare also useful for determining a relationship between aphakic ocularpower and ELP (e.g., estimated ELP). In such cases, it may beadvantageous for both the corneal power and axial length data of thesample eyes to span the respective meaningful ranges of these valuesfound in the population in a statistically-meaningful way. In someembodiments, if the relationship between aphakic ocular power andestimated ELP is determined using calculated theoretical aphakic ocularpower values, it can be later modified, improved, or refined based onactual aphakic ocular power measurements using, for example regressionanalysis.

The estimated ELP values illustrated in FIG. 2 were calculated from thecorneal power and axial length data for the eyes using the Holladay 1formula, though, as described herein, other formulas can also be used.In addition, actual measured ELP values obtained postoperatively (e.g.,by ultrasound or OCT) could also have been used in order to establishthe relationship between aphakic ocular power and ELP (e.g., measuredELP).

The aphakic ocular power data and the estimated ELP data were correlatedin order to determine a mathematical relationship between the two setsof data. In particular, least squares regression techniques were used toidentify a fitted curve 230 that adequately describes the relationshipbetween the two sets of data. However, many different techniques fordetermining relationships between the aphakic ocular power and estimatedELP data, and/or for calculating estimated ELP values from aphakicocular power values, can be used, including various types of regressionanalysis, curve fitting techniques, neural networks, fuzzy logic, lookuptables, etc.

In some embodiments, the curve 230 is a cubic polynomial, as indicatedin FIG. 2, though other degrees of polynomials or types of functions canalso be used. The curve 230 generally slopes downward from left toright, indicating that eyes with relatively high aphakic ocular powerare estimated to have shorter effective lens positions than eyes withrelatively low amounts of aphakic ocular power. The fitted curve 230shows the empirical relationship between the aphakic ocular power dataand the estimated ELP values for each of the eyes. Thus, the equation ofthe curve 230 can be used to determine an estimated ELP value for an IOLimplanted into an eye having a specified aphakic ocular power. Theequation of the curve 230 is of the form y=ax³+bx²+cx+d, where a, b, c,and d are constants. In the equation, y corresponds to the estimated ELPvalue for the eye and it is written as a function of x, whichcorresponds to the aphakic ocular power of the eye.

For the particular IOL type, measurement units, and sample set of eyesthat were used, the equation of the fitted curve 230 was found to bey=−0.0014x³+0.0569x²−0.9255x+9.2168, though the constants a, b, c, and dwill vary depending, for example, on these factors. In some embodiments,the relationship between aphakic ocular power and estimated ELP usingthe Holladay 1 formula can be described by a line, a quadraticpolynomial, or a higher-order polynomial.

As indicated on the plot 200, there is a strong correlation between theaphakic ocular power and the estimated ELP values (R²=0.9912), thusindicating that aphakic ocular power is a good explanatory variable forestimated ELP. The relatively high degree of correlation between thesevalues is an advantageous result. While certain ELP formulas (includingthe Holladay 1 formula) have been verified to demonstrate a meaningfulrelationship between ELP on the one hand and corneal power and axiallength on the other hand, and while aphakic ocular power likewisedepends on corneal power and axial length, it does not necessarilymathematically follow that there is a well-defined, meaningfulrelationship between ELP and aphakic ocular power. Nevertheless, FIG. 2illustrates that such a relationship does in fact exist.

One feature, for example, of such a well-defined relationship is that amathematical function (e.g., a line or higher-order polynomial curve,etc.) can be found to relate ELP and aphakic ocular power values with anadequate degree of correlation (e.g., a minimum R² value overrepresentative ranges of ELP, for example measured in millimeters, andaphakic ocular power, for example measured in diopters). For example, insome embodiments, the R² value is at least 0.925. In some embodiments,the R² value is at least 0.950. In some embodiments, the R² value is atleast 0.975. In some embodiments, the R² value is at least 0.990.

The existence of a well-defined, meaningful relationship between aphakicocular power and validated estimates of ELP (e.g., those calculatedusing formulas such as the Holladay 1, Holladay 2, Hoffer Q, and SRK/Tformulas, etc.) allows for IOL power to be calculated from aphakicrefractive power without relying on corneal power (e.g., corneal Ks)and/or axial length measurements but while still maintaining theadvantages associated with using a validated ELP estimate in the IOLpower calculation.

Certain formulas for estimating ELP (including the Holladay 1) mayemploy correction modifiers which place certain limits on the magnitudeof the ELP estimate or otherwise modify it. For example, certain ELPestimation formulas include correction modifiers to limit the estimatedELP for relatively long eyes due to physiological reasons (e.g., the ELPnot being expected to be greater than 7 mm behind the cornea). For longeyes the ELP may not be as large as a linear relationship between axiallength of a particular eye compared to that of the average eye mayindicate. The degree to which the ELP is modified may depend on theoverall size of the eye, which can be indicated by the corneal diameter,sometimes referred to as the white-to-white distance. This parameter canbe used, for example in conjunction with aphakic ocular power, todetermine or modify an estimate of ELP. This can be done, for example,by regression analysis. Other ocular characteristics can also be used,for example in conjunction with aphakic ocular power, to determine ormodify an estimate of ELP.

FIG. 3 is a plot 300 of estimated ELP versus aphakic ocular power forthe sample group of eyes, the estimated ELP having been determined usingthe Holladay 1 formula and corrected to reduce errors attributable torelatively long axial length. As in FIG. 2, the estimated ELP values areplotted on the axes as a function of spherical equivalent aphakic ocularpower. The aphakic ocular power values and estimated ELP values for thesample set of eyes can be obtained similarly as described with respectto FIG. 2. In addition, the aphakic ocular power values and estimatedELP values can be correlated using techniques similar to those describedwith respect to FIG. 2.

In FIG. 3, the aphakic ocular power data and the estimated ELP data werecorrelated in order to determine a mathematical relationship between thetwo sets of data. In particular, least squares regression techniqueswere used to identify a fitted curve 330. In some embodiments, the curve330 is a cubic polynomial, as indicated in FIG. 3, though other degreesof polynomials or types of functions can also be used. The curve 330shows that the long eye correction disproportionately affected theestimated ELP values for eyes with relatively strong aphakic ocularpower (the ELP estimates for the highest powered aphakic eyes increasedfrom about 3.25 mm in FIG. 2 to about 4.75 mm in FIG. 3) as compared tothe eyes with weaker aphakic ocular power (the ELP estimates for thelowest powered aphakic eye decreased from about 7.25 mm in FIG. 2 toabout 6.5 mm in FIG. 3). As noted, the overall effect of the long eyecorrection was to increase ELP estimates for higher-powered aphakic eyesand to decrease the ELP estimates for lower-powered aphakic eyes, thuscompressing the estimated ELP values into a tighter range.

The fitted curve 330 shows the empirical relationship between theaphakic ocular power data and the long eye-corrected estimated ELPvalues for each of the eyes. Thus, the equation of the curve 330 can beused to determine a long eye-corrected estimated ELP value for an IOLimplanted into an eye having a specified aphakic ocular power. Theequation of the curve 330 in FIG. 3 isy=−0.001x³−0.0353x²+0.2314x+4.8837, though the constants a, b, c, and dwill vary depending, for example, on measurement units, the sample data,IOL type, etc. In some embodiments, the relationship between aphakicocular power and estimated ELP using the Holladay 1 formula is describedby a line, a quadratic polynomial, or a higher-order polynomial.

As indicated on the plot 300, the correlation between the aphakic ocularpower and the long eye-corrected estimated ELP values is slightly lowerthan the correlation between aphakic ocular power and the uncorrectedestimated ELP values (R²=0.95 versus R²=0.9912). However, thecorrelation is still relatively strong, thus indicating that aphakicocular power is a good explanatory variable for long eye-correctedestimated ELP.

FIG. 4 is a plot 400 of three different types of estimated ELP versusaphakic ocular power for the sample group of eyes, the three differenttypes of estimated ELP being the Holladay 1 formula, the SRK/T formula,and the Hoffer Q formula. The ELP estimates in FIG. 4 are longeye-corrected, but this is not required. The aphakic ocular power dataand the estimated ELP data can be collected and analyzed in ways similarto those described with respect to the preceding figures.

FIG. 4 shows a comparison of ELP estimates calculated using the Holladay1, the SRK/T, and the Hoffer Q formulas. The Holladay 1 estimates areplotted as a function of aphakic ocular power and are represented on theplot 400 as diamonds. A fitted curve 430 for the Holladay 1 data isshown with a dashed line. The equation of the fitted curve 430 was foundto be y=−0.001x³−0.036x²+0.2441x+5.9229, though the constants a, b, c,and d will vary, for example, depending on previously-mentioned factors.In some embodiments, the relationship between aphakic ocular power andestimated ELP using the Holladay 1 formula can be described by a line, aquadratic polynomial, or a higher-order polynomial. The correlationbetween aphakic ocular power and estimated ELP for the Holladay 1estimates was relatively strong (R²=0.95).

The SRK/T estimates are plotted as a function of aphakic ocular powerand are represented on the plot 400 as squares. A fitted curve 450 forthe SRK/T data is shown with a dotted line. The equation of the fittedcurve 450 was found to be y=−0.0003x³+0.012x²−0.33302x+8.0596, thoughthe constants a, b, c, and d will vary, for example, depending onpreviously-mentioned factors. In some embodiments, the relationshipbetween aphakic ocular power and estimated ELP using the SRK/T formulacan be described by a line, a quadratic polynomial, or a higher-orderpolynomial. The correlation between aphakic ocular power and estimatedELP for the SRK/T estimates was relatively strong (R²=0.94).

The Hoffer Q estimates are plotted as a function of aphakic ocular powerand are represented on the plot 400 as triangles. A fitted curve 440 forthe Hoffer Q data is shown with a solid line. The equation of the fittedcurve 440 was found to be y=−0.0001x³+0.0056x²−0.1913x+7.0336, thoughthe constants a, b, c, and d will vary, for example, depending onpreviously-mentioned factors. In some embodiments, the relationshipbetween aphakic ocular power and estimated ELP using the Hoffer Qformula can be described by a line, a quadratic polynomial, or ahigher-order polynomial. The correlation between aphakic ocular powerand estimated ELP for the Hoffer Q estimates was relatively strong(R²=0.94).

As indicated in FIG. 4, the correlation between aphakic ocular power andestimated ELP was relatively strong for each of the three ELP formulastested. Thus, while the results for the three formulas are different,aphakic ocular power is seen to be a good explanatory variable for ELPestimates calculated using the Holladay 1, the SRK/T, and the Hoffer Qformulas.

As discussed herein, aphakic ocular power is dependent upon cornealpower and axial length. The dependencies of aphakic ocular power (e.g.,spherical equivalent aphakic ocular power) on axial length and cornealcurvature are illustrated in FIGS. 5 and 6, respectively. Axial lengthmeasurement values and corneal curvature measurement values (e.g.,average corneal curvature) were obtained for a set of eyes. The axiallength measurement values span the range from about 20.5 mm to about27.5 mm. The corneal curvature values span the range from about 35diopters to about 52 diopters. The axial length and corneal curvaturemeasurement values were used to calculate theoretical aphakic ocularpower values for each of the tested eyes.

FIG. 5 is a plot 500 of aphakic ocular power versus axial length. Theaphakic ocular power values are plotted as a function of axial length,with a constant K value, and are indicated by the diamonds on the plot500. A fitted line 560 was calculated using the techniques describedherein. The fitted line 560 represents the mathematical relationshipbetween axial length and aphakic ocular power. The equation of the linewas found to be y=−2.3594x+69.369. As indicated in FIG. 5, thecorrelation between aphakic ocular power and axial length was very goodover this range (R²=0.9929), indicating that axial length is a very goodpredictor of aphakic ocular power.

FIG. 6 is a plot 600 of aphakic ocular power versus corneal curvature.The aphakic ocular power values are plotted as a function of cornealcurvature (e.g., average corneal curvature), with a constant axiallength, and are indicated by the diamonds on the plot 600. A fitted line670 was calculated using the techniques described herein. The fittedline 670 represents the mathematical relationship between the cornealcurvature and aphakic ocular power. The equation of the line was foundto be y=−0.9998x+56.904. As indicated in FIG. 6, the correlation betweenaphakic ocular power and corneal curvature was essentially perfect overthis range (R²=1), indicating that corneal curvature is a very goodpredictor of aphakic ocular power.

With reference to FIGS. 5 and 6, the dependence of aphakic ocular power(e.g., spherical equivalent aphakic ocular power) on axial length wassomewhat stronger than its dependence upon corneal curvature, asindicated by the greater magnitude slope of the fitted line 560 ascompared to the fitted line 670. Thus, in some embodiments, it isadvantageous to determine which of the various ELP estimation formulasexhibits the strongest correlation with axial length measurements. Theselected ELP estimation formula can be used to determine therelationship between aphakic ocular power and ELP, as described herein.This relationship can then be used to determine an estimate of ELP foran IOL in a patient's eye given the intraoperatively-measured aphakicocular power of the patient's eye. Finally, this estimate can be used inthe calculation of IOL power, as described herein.

FIG. 7 is a plot 700 of three different types of estimated ELP versusaxial length, the three different types of estimated ELP being theHolladay 1 formula, the SRK/T formula, and the Hoffer Q formula. TheHolladay 1 data is illustrated on the plot 700 by diamonds, the SRK/Tdata by squares, and the Hoffer Q data by triangles. As illustrated inFIG. 7, of the three tested ELP estimation formulas, the Hoffer Q ELPestimates exhibited the closest correlation with axial length(R²=0.9375). Thus, in some embodiments, the Hoffer Q ELP estimationformula is used in the determination of the relationship between aphakicocular power and ELP estimates. As disclosed herein, this relationshipcan be used to calculate an ELP estimate for an IOL to be implanted in apatient's eye given the aphakic ocular power of the patient's eye. ThisELP estimate is useful in the determination of IOL power. While theHoffer Q ELP estimation formula is used to calibrate the relationshipbetween aphakic ocular power and estimated ELP in some embodiments, itshould be understood that other ELP estimation formulas, such as theHolladay 1, Holladay 2, SRK/T, etc., can also be used for this purpose.In addition, the relationship between aphakic ocular power and ELP thatis established using any given ELP estimation formula can be modified orenhanced based on, for example, another ELP estimation formula or onactual post-operative ELP measurements. As discussed herein, theindications of aphakic ocular power that are used to establish therelationship with ELP can be, for example, calculated theoreticalaphakic ocular power values or actual intraoperative aphakicmeasurements.

In some embodiments, it may be advantageous to determine which of thevarious ELP estimation formulas exhibits the strongest correlation withthe corneal curvature measurements. This can be done by, for example,determining the correlation between ELP estimates from the variousformulas and corneal curvature, similar to what is illustrated in FIG. 7with respect to axial length. As described herein, the selected ELPestimation formula can be used to determine a relationship betweenaphakic ocular power and estimated ELP, which is then useful in thedetermination of IOL power.

FIGS. 1-7 have illustrated, among other things, mathematicalrelationships between aphakic ocular power and ELP estimation valuescalculated for a particular type of IOL. The type of IOL can affect ELPestimates by virtue of, for example, a manufacturer-recommended constantassociated with the particular IOL. The manufacturer-recommendedconstant may be, for example, an A-constant for the particular IOL(e.g., in the case of the SRK/T formula), the manufacturer's anteriorchamber depth (ACD) (e.g., in the case of the Hoffer Q formula), etc.The equipment and procedures described herein, however, are not limitedto any particular type of IOL. Therefore, it would be advantageous tocalculate a mathematical relationship between aphakic ocular power(e.g., spherical equivalent aphakic ocular power) and estimated ELP thatis independent from, or less dependent upon, any particular type of IOL.

A manufacturer-recommended constant for an IOL represents variations inIOL power selection and/or ELP estimation for the lens due to, forexample, the lens style and material. For example, different IOLs may bemade of different materials that affect its performance, or a particularIOL may have a tendency to sit differently in the capsular bag of thepatient's eye (as compared to other IOLs) depending upon its structuraldesign. The A-constant, or other manufacturer-recommended constant, ofthe IOL is used in ELP estimates and IOL power calculations to accountfor such lens-specific variations.

FIG. 8 is a plot 800 of estimated ELP versus aphakic ocular power forthe sample group of eyes, the estimated ELP having been determined usingthe Hoffer Q formula and adjusted by reducing the effect of themanufacturer's constant for the particular IOL on the result. Forexample, the effect of the manufacturer's constant for the IOL can besubstantially nulled by subtracting it from the ELP estimate. Theadjusted relationship between aphakic ocular power and estimated ELPthat remains can be added to the manufacturer's constant for any IOL toarrive at an IOL-specific ELP estimate for that lens and the patient'sspecific aphakic ocular refraction. Mathematical relationships betweenaphakic ocular power and estimated ELP that are derived using other ELPestimation formulas can be similarly adjusted to reduce the effect ofmanufacturer constants.

The adjusted ELP estimates are plotted on the axes as a function ofaphakic ocular power. These values are indicated as diamonds on the plot800. The aphakic ocular power data and the adjusted ELP estimates werecorrelated in order to determine a mathematical relationship between thetwo sets of data. In particular, a fitted curve 840 was calculated. Insome embodiments, the fitted curve 840 is a cubic polynomial, asindicated in FIG. 8, though other degrees of polynomials or types offunctions can also be used. The fitted curve 840 shows the empiricalrelationship between the aphakic ocular power data and the adjustedHoffer Q ELP estimates for each of the eyes. Thus, the equation of thefitted curve 840 can be used to determine an adjusted ELP estimate givena particular aphakic ocular power value, the adjusted ELP estimatehaving reduced dependence upon, or being substantially independent from,the manufacturer's constant for any particular IOL.

The equation of the curve 840 was calculated asy=−0.0001x³+0.0055x²−0.1902x+1.8314, though the coefficients may varydepending upon the sample set of eyes and other factors. In someembodiments, the relationship between aphakic ocular power andA-constant-adjusted ELP estimates using the Hoffer Q formula can bedescribed by a line, a quadratic polynomial, or a higher-orderpolynomial.

Upon comparison of the Hoffer Q fitted curve 840 to the Hoffer Q fittedcurve 440 from FIG. 4, it is noted that the equations for the two curvesgenerally differ by an additive constant of 7.0336−1.8314=5.2022. Thisadditive constant corresponds to the manufacturer's constant for the IOLfor which the ELP estimates in FIG. 4 were calculated. Thus, adjustedHoffer Q ELP estimates calculated using the mathematical relationshipgiven in FIG. 8 are less dependent upon any particular choice of IOLthan are the Hoffer Q ELP estimates given by the relationship in FIG. 4.Accordingly, a Hoffer Q ELP estimate can be calculated from aphakicocular power for any choice of IOL using, for example, the relationshipin FIG. 8. An IOL-specific Hoffer Q ELP estimate can then be obtainedby, for example, adding or subtracting the manufacturer's constant forthe selected IOL. Similar adjustments for manufacturer's constants canbe applied to mathematical relationships calculated to relate aphakicocular power to estimated ELP based on other ELP estimation formulas,including the Holladay 1, Holladay 2, and SRK/T formulas.

In a similar way, the mathematical relationships between aphakic ocularpower and estimated ELP can also be corrected for a surgeon factor whichrepresents variations in IOL power calculation and/or ELP estimation dueto, for example, surgical technique and the particular measurementdevices used by the surgeon. Such adjustments can also be applied, forexample, to mathematical relationships between aphakic ocular power andestimated ELP that are determined using actual post-surgical ELPmeasurements rather than ELP estimation formulas. Other factors can alsobe used to adjust ELP estimates.

While a relationship between ELP and aphakic ocular power can bedetermined by correlating aphakic ocular power values with ELP estimatescalculated using estimation formulas such as those mentioned herein,this is not required. For example, a relationship between ELP andaphakic ocular power could be determined, for example, using regressionanalysis of measured post-operative ELP values and aphakic ocular powervalues (whether measured intra-operatively or calculated theoreticallyfrom other data) for a sample set of eyes. In addition, relationshipscan be found between ELP and aphakic ocular power in combination withone or more other ocular characteristics (e.g., white-to-white distancevalues). For example, regression analysis could be used to determine anempirical relationship between aphakic ocular power values andwhite-to-white distance values on the one hand, and ELP values (whethermeasured postoperatively or estimated by a formula) on the other hand.Relationships between aphakic ocular power and ELP can be found usingcombinations of measured and theoretical aphakic ocular power values,and combinations of post-operative measured ELP values and calculatedELP estimates.

Embodiments have been described in connection with the accompanyingdrawings. However, it should be understood that the figures are notdrawn to scale. Distances, angles, etc. are merely illustrative and donot necessarily bear an exact relationship to actual dimensions andlayout of the devices illustrated. In addition, the foregoingembodiments have been described at a level of detail to allow one ofordinary skill in the art to make and use the devices, systems, etc.described herein. A wide variety of variation is possible. Components,elements, and/or steps may be altered, added, removed, or rearranged.While certain embodiments have been explicitly described, otherembodiments will become apparent to those of ordinary skill in the artbased on this disclosure.

The systems and methods described herein can advantageously beimplemented using, for example, computer software, hardware, firmware,or any combination of software, hardware, and firmware. Software modulescan comprise computer executable code for performing the functionsdescribed herein. In some embodiments, computer-executable code isexecuted by one or more general purpose computers. However, a skilledartisan will appreciate, in light of this disclosure, that any modulethat can be implemented using software to be executed on a generalpurpose computer can also be implemented using a different combinationof hardware, software, or firmware. For example, such a module can beimplemented completely in hardware using a combination of integratedcircuits. Alternatively or additionally, such a module can beimplemented completely or partially using specialized computers designedto perform the particular functions described herein rather than bygeneral purpose computers. In addition, where methods are described thatare, or could be, at least in part carried out by computer software, itshould be understood that such methods can be provided oncomputer-readable media (e.g., optical disks such as CDs or DVDs, harddisk drives, flash memories, diskettes, or the like) that, when read bya computer or other processing device, cause it to carry out the method.

A skilled artisan will also appreciate, in light of this disclosure,that multiple distributed computing devices can be substituted for anyone computing device illustrated herein. In such distributedembodiments, the functions of the one computing device are distributedsuch that some functions are performed on each of the distributedcomputing devices.

While certain embodiments have been explicitly described, otherembodiments will become apparent to those of ordinary skill in the artbased on this disclosure. Therefore, the scope of the invention isintended to be defined by reference to the claims and not simply withregard to the explicitly described embodiments.

1. A method for determining the optical power of an intraocular lens tobe inserted into the eye of a patient, the method comprising: receivingas an input an indication of the aphakic refractive power of thepatient's eye; determining, with a processor, an estimate of thepost-surgical effective lens position (ELP) of the intraocular lens forthe patient's eye, the estimate being based on the indication of theaphakic refractive power of the patient's eye and on a relationshipbetween aphakic refractive power and post-surgical intraocular lens ELP;and determining an amount of optical power for the intraocular lens tobe inserted into the patient's eye based on the estimate of thepost-surgical ELP of the intraocular lens in the patient's eye.
 2. Themethod of claim 1, wherein the relationship between aphakic refractivepower and post-surgical intraocular lens ELP is determined usingregression analysis.
 3. The method of claim 1, wherein the estimate ofthe post-surgical ELP of the intraocular lens is not based on measuredcorneal power of the patient's eye.
 4. The method of claim 1, whereinthe estimate of the post-surgical ELP of the intraocular lens is notbased on measured axial length of the patient's eye.
 5. The method ofclaim 1, wherein the indication of the aphakic refractive power of thepatient's eye comprises an intraoperative measurement of the aphakicrefractive power of the patient's eye.
 6. The method of claim 5, whereinthe intraoperative measurement of the aphakic refractive power of thepatient's eye comprises the spherical equivalent power of the patient'seye.
 7. The method of claim 1, further comprising outputting theestimate of the post-surgical ELP of the intraocular lens.
 8. The methodof claim 1, further comprising outputting the amount of optical powerfor the intraocular lens.
 9. The method of claim 1, wherein the estimateof the post-surgical ELP of the intraocular lens is based on theintraocular lens being inserted into the capsular bag of the patient'seye.
 10. The method of claim 1, wherein determining the estimate of thepost-surgical ELP of the intraocular lens comprises calculating theestimate using a mathematical function that comprises the relationshipbetween aphakic refractive power and intraocular lens ELP.
 11. Amachine-readable medium that, when read by a machine, causes the machineto perform a method comprising: receiving as an input an indication ofthe aphakic refractive power of the patient's eye; determining anestimate of the post-surgical effective lens position (ELP) of theintraocular lens based on the indication of the aphakic refractive powerof the patient's eye and on a relationship between aphakic refractivepower and intraocular lens ELP; and determining an appropriate amount ofoptical power for the intraocular lens to be inserted into the eye ofthe patient based on the estimate of the post-surgical ELP of theintraocular lens.
 12. An ophthalmic method for determining arelationship between post-surgical effective lens position (ELP) of anintraocular lens and aphakic ocular power, the method comprising:obtaining a plurality of indications of the aphakic power of arespective plurality of eyes; determining a plurality of indications ofthe post-surgical ELP of an intraocular lens for the respectiveplurality of eyes; and determining a relationship between the pluralityof indications of the aphakic power and the plurality of indications ofthe post-surgical ELP using a processor.
 13. The method of claim 12,wherein the plurality of indications of aphakic power of the respectiveplurality of eyes comprise a plurality of aphakic measurements of theaphakic power of the respective plurality of eyes.
 14. The method ofclaim 12, wherein the plurality of indications of aphakic power of therespective plurality of eyes comprise a plurality of calculated valuesbased on the respective corneal power and axial length of the respectiveplurality of eyes.
 15. The method of claim 12, wherein determining aplurality of indications of the post-surgical ELP of an intraocular lensfor the respective plurality of eyes comprises performing post-surgicalmeasurements of the ELP for the respective plurality of eyes.
 16. Themethod of claim 12, wherein determining a plurality of indications ofthe post-surgical ELP of an intraocular lens for the respectiveplurality of eyes comprises using an ELP estimation formula for therespective plurality of eyes.
 17. The method of claim 16, wherein theELP estimation formula comprises the Holladay 1, the Holladay 2, theSRK/T, the Hoffer Q, or the Hagis formula.
 18. The method of claim 12,wherein determining a relationship between the plurality of indicationsof the aphakic power and the plurality of indications of thepost-surgical ELP comprises mathematically modeling the relationshipbetween the plurality of indications of aphakic power and the pluralityof indications of the post-surgical ELP of the intraocular lens.
 19. Themethod of claim 18, wherein mathematically modeling the relationshipcomprises using regression analysis of the plurality of indications ofthe aphakic power for the respective plurality of eyes and the pluralityof indications of the post-surgical ELP of an intraocular lens for therespective plurality of eyes to determine the relationship.
 20. Themethod of claim 19, wherein using regression analysis comprises fittinga polynomial function whose independent variable corresponds to theplurality of indications of the aphakic power for the respectiveplurality of eyes and whose dependent variable corresponds to theplurality of indications of the post-surgical ELP of the intraocularlens for the respective plurality of eyes.
 21. An ophthalmic instrumentcomprising: a measurement device for measuring the aphakic power of apatient's eye; and a processor for performing a method comprising,receiving an indication of the aphakic refractive power of the patient'seye from the measurement device, determining an estimate of thepost-surgical effective lens position (ELP) of an intraocular lens to beinserted in the patient's eye, the estimate of the post-surgical ELP ofthe intraocular lens being based on the indication of the aphakicrefractive power of the patient's eye and a general relationship betweenaphakic refractive power and intraocular lens ELP, and determining anappropriate amount of optical power for the intraocular lens to beinserted into the patient's eye based on the estimate of thepost-surgical ELP of the intraocular lens.
 22. The ophthalmic instrumentof claim 21, wherein the measurement device comprises a wavefrontaberrometer.
 23. The ophthalmic instrument of to claim 22, wherein thewavefront aberrometer comprises a Talbot-moiré wavefront aberrometer.